Snowmobile skis often have elongated steering skags carried on the bottom for the ski that act as a narrow type of keel to increase the bite of the ski into the snow when the ski is turned. Skis and skags leave an impression in the snow corresponding to the bottom profile of the ski and skag. Particularly in wet or compacted snow, a snowmobile ski coming upon the impression left by a previous snowmobile ski will tend to follow the same track (especially if the temperature has dropped causing the wet snow to freeze). This effect is known as tracking or darting. Darting forces the snowmobile operator to compensate or correct for the tracking steering forces by over-steering the vehicle to maintain directional stability. Darting can be quite severe particularly if the snow containing the initial track was wet and has refrozen (such as on a sunny winter day followed by a cold night—typical snowmobiling weather).
The skag of a snowmobile following such a track will naturally situate itself in the previous impression and a considerable effort is required to steer out of such a track. Over time, darting can cause the driver to become fatigued from the effort of steering. In addition, the snowmobile may feel unstable due to the frequent abrupt directional changes experienced with darting. A need exists, therefore, for a snowmobile ski that reduces the problem of darting.
U.S. Pat. No. 5,836,594, issued to Simmons discloses a snowmobile ski having a downwardly extending longitudinal side portion on each side of the middle portion of the snowmobile ski. The longitudinal side portions are formed from the sides of the snowmobile ski extending downwardly. The downwardly extending longitudinal side portions of the ski are centrally located along the length of the ski. As the downwardly extending longitudinal side portions descend, the outside wall of each such downwardly extending longitudinal side portion tapers inward. A metal guide rod is attached to, and runs longitudinally along, the bottom of each of the downwardly extending longitudinal side portions at the edge of the bottom of the downwardly extending longitudinal side portion.
At least two other skis are available that include dual skags. Those skis do not adequately solve the darting problem and also suffer various drawbacks. The prior art ski shown in FIGS. 1A–1C includes a dual runner skag for attachment to the bottom surface of a generally flat bottom ski. The dual runner skag includes two wear bars attached at the outside bottom edges of a flat plate. The plate and skags are typical of the prior art in that they extend along a significant length (if not the entire length) of the bottom surface of the ski. The long wear bar and skags can impair the steerability of the snowmobile. The prior art ski shown in FIGS. 2A–2B includes two round skags attached at the outer edges of the ski's keel. This ski, however, is exposed to considerable wear. In addition, debris can become lodged between the skags.